He is best known for his controversial book 1421: The Year China Discovered the World, in which he asserts that the fleets of Chinese Admiral Zheng Hevisited the Americas prior to European explorer Christopher Columbus in 1492, and that the same fleet circumnavigated the globe a century before the expedition of Ferdinand Magellan. Menzies' second book, 1434: The Year a Magnificent Chinese Fleet Sailed to Italy and Ignited the Renaissance extended his discovery hypothesis to the European continent. In his third book, The Lost Empire of Atlantis, Menzies claims that Atlantis did exist, in the form of the Minoan Civilization, and that it maintained a global seaborne empire extending to the shores of America and India, millennia before actual contact in the Age of Discovery.

In 1959, by his own account, Menzies was an officer on the HMS Newfoundland, on a voyage from Singapore to Africa, around the Cape of Good Hope, and on to the Cape Verde Islands and back to England. Menzies claims that the knowledge of the winds, currents, and sea conditions that he gained on this voyage was essential to reconstructing the 1421 Chinese voyage that he discusses in his first book.[15] Critics have challenged the depth of his nautical knowledge.[16] In 1969, Menzies was involved in an incident in the Philippines, when the Rorqual rammed a U.S. Navyminesweeper, the USS Endurance, which was moored at a pier. This collision punched a hole in the Endurance but did not damage the Rorqual. The ensuing enquiry found Menzies and one of his subordinates responsible for a combination of factors that led to the accident, including the absence of the coxswain (who usually takes the helm in port) who had been replaced by a less experienced crew member, and technical issues with the boat's telegraph.[11][17]

In 2002, Menzies published his first book: 1421: The Year China Discovered the World (published as 1421: The Year China Discovered America in the United States). The book is written informally, as a series of vignettes of Menzies' travels around the globe examining what he claims is evidence for his "1421 hypothesis", interspersed with speculation[6] and description of the achievements of AdmiralZheng He's fleet. Menzies states in the introduction that the book is an attempt to answer the question:

On some early European world maps, it appears that someone had charted and surveyed lands supposedly unknown to the Europeans. Who could have charted and surveyed these lands before they were 'discovered'?

In the book, Menzies concludes that only China had the time, money, manpower and leadership to send such expeditions and then sets out to prove that the Chinese visited lands unknown in either China or Europe. He claims that from 1421 to 1423, during the Ming Dynasty of China under EmperorZhu Di the fleets of Admiral Zheng He, commanded by the Chinese captainsZhou Wen, Zhou Man, Yang Qing, and Hong Bao, discovered Australia, New Zealand, the Americas, Antarctica, and the Northeast Passage; circumnavigated Greenland, tried to reach the North and South Poles, and circumnavigated the world before Ferdinand Magellan. The book has been published in many languages and countries around the world[26] and was listed as a New York Times best seller for several weeks in 2003.[27] Although the book contains numerous footnotes, references and acknowledgments, critics point out that it lacks supporting references for Chinese voyages beyond East Africa, the location acknowledged by professional historians as the limit of the fleet's travels.[28] Menzies bases his main theory on original interpretations and extrapolations of academic studies of minority population DNA, archaeological finds and ancient maps.

Menzies claims that knowledge of Zheng He's discoveries was subsequently lost because the Mandarin bureaucrats of the Imperial court feared that the costs of further voyages would ruin the Chinese economy. He conjectures that when Zhu Di died in 1424 and the new Hongxi Emperor forbade further expeditions, the Mandarins hid or destroyed the records of previous exploration to discourage further voyages. Tan Ta Sen, president of the International Zheng He Society, has acknowledged the book's popular appeal as well as its scholarly failings:

The book is very interesting, but you still need more evidence. We don't regard it as an historical book, but as a narrative one. I want to see more proof. But at least Menzies has started something, and people could find more evidence.[29]

Within the academic world, the book (and Menzies' "1421 hypothesis") is dismissed by sinologists and professional historians.[30][31][32] In 2004, historian Robert Finlay severely criticized Menzies in the Journal of World History for his "reckless manner of dealing with evidence" that led him to propose hypotheses "without a shred of proof".[6] Finlay wrote:

Unfortunately, this reckless manner of dealing with evidence is typical of 1421, vitiating all its extraordinary claims: the voyages it describes never took place, Chinese information never reached Prince Henry and Columbus, and there is no evidence of the Ming fleets in newly discovered lands. The fundamental assumption of the book—that Zhu Di dispatched the Ming fleets because he had a "grand plan", a vision of charting the world and creating a maritime empire spanning the oceans—is simply asserted by Menzies without a shred of proof ... The reasoning of 1421 is inexorably circular, its evidence spurious, its research derisory, its borrowings unacknowledged, its citations slipshod, and its assertions preposterous ... Examination of the book's central claims reveals they are uniformly without substance.[33]

A group of scholars and navigators—Su Ming Yang of the United States, Jin Guo-Ping of Portugal, Philip Rivers of Malaysia, and Malhão Pereira and Geoff Wade of Singapore—questioned Menzies' methods and findings in a joint message:[28]

His book 1421: The Year China Discovered the World, is a work of sheer fiction presented as revisionist history. Not a single document or artifact has been found to support his new claims on the supposed Ming naval expeditions beyond Africa...Menzies' numerous claims and the hundreds of pieces of "evidence" he has assembled have been thoroughly and entirely discredited by historians, maritime experts and oceanographers from China, the U.S., Europe and elsewhere.[28]

1434: The Year a Magnificent Chinese Fleet Sailed to Italy and Ignited the Renaissance[edit]

In 2008 Menzies released a second book entitled 1434: The Year a Magnificent Chinese Fleet Sailed to Italy and Ignited the Renaissance. In it Menzies claims that in 1434 Chinese delegations reached Italy and brought books and globes that, to a great extent, launched the Renaissance. He claims that a letter written in 1474 by Paolo dal Pozzo Toscanelli and found amongst the private papers of Columbus indicates that an earlier Chinese ambassador had direct correspondence with Pope Eugene IV in Rome. Menzies then claims that materials from the Chinese Book of Agriculture, the Nong Shu, published in 1313 by the Yuan-dynasty scholar-official Wang Zhen (fl. 1290–1333), were copied by European scholars and provided direct inspiration for the illustrations of mechanical devices which are attributed to the Italian Renaissance polymaths Taccola (1382–1453) and Leonardo da Vinci (1452–1519).

Felipe Fernández-Armesto, a professor of history at Tufts University in the United States and at Queen Mary, University of London, examined Menzies' claim that private papers of Columbus indicate a Chinese ambassador in correspondence with the Pope and called this claim "drivel." He states that no reputable scholar supports the view that Toscanelli's letter refers to a Chinese ambassador.[2]Martin Kemp, Professor of the History of Art at Oxford University, questions the rigor of Menzies' application of the historical method, and in regard to European illustrations purporting to be copied from the Chinese Nong Shu, writes that Menzies "says something is a copy just because they look similar. He says two things are almost identical when they are not."[2]

In regard to Menzies' theory that Taccola's sketches are based on Chinese information, Captain P.J. Rivers writes that Menzies contradicts himself by saying elsewhere in his book that Taccola had started his work on his technical sketches in 1431, when Zheng He's fleet was still assembled in China, and that the Italian engineer finished his technical sketches in 1433—one year before the purported arrival of the Chinese fleet.[34] Geoff Wade, a senior research fellow at the Asia Research Institute of the National University of Singapore, acknowledges that there was a cross exchange of technological ideas between Europe and China, but ultimately classifies Menzies' book as historical fiction and asserts that there is "absolutely no Chinese evidence" for a maritime venture to Italy in 1434.[2]